1. Field of the Invention
The invention is related to a process for the thermal hydrogenation conversion of heavy hydrocarbon feedstocks.
2. Description of the Related Art
As the world's supply of crude oil becomes heavier and contains higher sulfur levels, there is a challenge is to meet the growing demand for light, high-quality, low-sulfur transportation fuels. The upgrading of heavy hydrocarbon feedstocks may help to meet this demand. Several processes are useful for upgrading heavy hydrocarbon feedstocks. One such process is known as slurry phase hydrocracking. Slurry-phase hydrocracking converts any hydrogen and carbon containing feedstock derived from mineral oils, synthetic oils, coal, biological processes, and the like, hydrocarbon residues, such as vacuum residue (VR), atmospheric residue (AR), deasphalted bottoms, coal tar, and the like, in the presence of hydrogen under high temperatures and high pressures, for example, from about 750° F. (400° C.) up to about 930° F. (500° C.), and from about 1450 psig (10,000 kPa) up to about 4000 psig (27,500 kPa), or higher. To prevent excessive coking during the reaction, finely powdered additive particles made from carbon, iron salts, or other materials, may be added to the liquid feed. Inside the reactor, the liquid/powder mixture ideally behaves as a single homogenous phase due to the small size of the additive particles. In practice, the reactor may be operated as an up-flow bubble column reactor or as a circulating ebullated bed reactor and the like with three phases due to the hydrogen make up and light reaction products contributing to a gas phase, and larger additive particles contributing to a solid phase, and the smaller additive particles, feedstock and heavier reaction products contributing to the liquid phase, with the combination of additive and liquid comprising the slurry. In slurry phase hydrocracking, feedstock conversion may exceed 90% into valuable converted products, and even more than 95% when a vacuum residue is the feedstock.
One example of slurry phase hydrocracking is known as Veba Combi-Cracking™ (VCC™) technology. This technology operates in a once through mode where in one embodiment of the process, a proprietary particulate additive is added to a heavy feedstock, such as VR, to form a slurry feed. The slurry feed is charged with hydrogen and heated to reactive temperatures to crack the vacuum residue into lighter products. The vaporized conversion products may or may not be further hydrotreated and/or hydrocracked in a second stage fixed bed catalyst reactor. It produces a wide range of distillate products including vacuum gas oil, middle distillate (such as diesel), naphtha and light gas.
It has been disclosed in various literature that the particulate additive for slurry phase hydrocrackers may include a wide range of materials. These materials reportedly include, but are not limited to, catalyst, red mud, iron (III) oxide, blast furnace dust, activated coke from hard coal or lignites, carbon black (soot), ashes from gasification processes of crude oil, silicon oxides and other inorganic minerals containing iron, such as laterite or limonite. The particulate additives are reported to have a wide particle size distribution between 0.1 and 2,000 microns, with a preference towards to lower to middle of the range. It has been reported that it is desirable to include between 10 and 40 wt % (weight percent) of the particles above 100 microns in size, with the balance of particles below 100 microns in size. To achieve finer control on the particle size distribution of the additive introduced into the process, a system has been proposed for introducing a fine particle size range and a coarse particle size range of additives separately into a mixing tank containing feed to obtain finer control on the relative size distribution of the additives mixed in with the feedstock. The slurry feedstock is then introduced into the high pressure pre-heat train with hydrogen and introduced into a reactor. See, e.g., U.S. Pat. No. 4,851,107, to Kretschmar et al. which is incorporated herein by reference.
Despite the various processes and alternatives available for upgrading heavy hydrocarbons, there is still a need for improving the existing processes to benefit the economics, efficiency and effectiveness of the unit operations.